Close examination

Restorer Jill Dunkerton delves into 'The Tribute Money'

About the video:

Find out about Titian's techniques, his careful planning, and his alterations and deliberations. National Gallery Restorer Jill Dunkerton explains how X-rays can reveal the artist's working practice. Featuring Titian's painting 'The Tribute Money'.

From the National Gallery DVD, 'Titian'

Find out more about Titian, The Tribute Money, about 1560-8 (perhaps begun in the 1540s)

Jill Dunkerton: Titian is an artist who, in his later career, spent a very long time on his paintings. At least, they were in his studio for a very long time. In his early paintings, we don’t know how fast he was. I think the actual process of laying on the paint wasn’t necessarily slow, but because he made all these alterations and he seems always to have made them on top of dry paint – he didn’t like working with a lot of wet painting – they must have been sitting around for quite a time while he was allowing the paint to dry.

Palma Giovane: He sketched his pictures with bold strokes made with brushes laden with colours. He then used to turn the painting to the wall and leave it there, sometimes for several months without looking at it. When taking the picture up again, he would examine it with the utmost rigour, as if it were his mortal enemy, and then set about correcting it.

Jill Dunkerton: If, in an X-ray, you see a lot of white colour, it could just mean that he’s painted something very, very solid and dense, for example, a white drapery. So, there’s lots of white, but on the whole, where you do have an alteration, you tend to see extra thicknesses of white, and they can jump out at you as being very obviously an area where changes have happened.

In the case of the painting of the head of the Pharisee, everything seems to have come right straight away. So, as a result, in the X-ray it’s a very, very dark, shadowy shape. That’s because there is very little lead white in the paint. Now of course, this is a figure in shadow, and so he’s not going to have as much lead white. His complexion isn’t going to be as fair. By contrast, the head of Christ is this extraordinary mask of white because there is so much lead white as a result of the alterations. Originally, Christ seems to have been painted with his head more inclined, tilted towards the Pharisee, rather as if he is listening to him. Perhaps a more human way, but Titian decided that he wanted to make his Christ more imposing, and so he shifts the head to its present upright position. That’s the back of the present head that we see there.

More from Beneath the brushstrokes (10 videos)

02:32

Close examination

Restorer Jill Dunkerton delves into 'The Tribute Money'

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About the video:

Find out about Titian's techniques, his careful planning, and his alterations and deliberations. National Gallery Restorer Jill Dunkerton explains how X-rays can reveal the artist's working practice. Featuring Titian's painting 'The Tribute Money'.

From the National Gallery DVD, 'Titian'

Find out more about Titian, The Tribute Money, about 1560-8 (perhaps begun in the 1540s)

Jill Dunkerton: Titian is an artist who, in his later career, spent a very long time on his paintings. At least, they were in his studio for a very long time. In his early paintings, we don’t know how fast he was. I think the actual process of laying on the paint wasn’t necessarily slow, but because he made all these alterations and he seems always to have made them on top of dry paint – he didn’t like working with a lot of wet painting – they must have been sitting around for quite a time while he was allowing the paint to dry.

Palma Giovane: He sketched his pictures with bold strokes made with brushes laden with colours. He then used to turn the painting to the wall and leave it there, sometimes for several months without looking at it. When taking the picture up again, he would examine it with the utmost rigour, as if it were his mortal enemy, and then set about correcting it.

Jill Dunkerton: If, in an X-ray, you see a lot of white colour, it could just mean that he’s painted something very, very solid and dense, for example, a white drapery. So, there’s lots of white, but on the whole, where you do have an alteration, you tend to see extra thicknesses of white, and they can jump out at you as being very obviously an area where changes have happened.

In the case of the painting of the head of the Pharisee, everything seems to have come right straight away. So, as a result, in the X-ray it’s a very, very dark, shadowy shape. That’s because there is very little lead white in the paint. Now of course, this is a figure in shadow, and so he’s not going to have as much lead white. His complexion isn’t going to be as fair. By contrast, the head of Christ is this extraordinary mask of white because there is so much lead white as a result of the alterations. Originally, Christ seems to have been painted with his head more inclined, tilted towards the Pharisee, rather as if he is listening to him. Perhaps a more human way, but Titian decided that he wanted to make his Christ more imposing, and so he shifts the head to its present upright position. That’s the back of the present head that we see there.

04:08

Paintings decoded

Artist John Lessore and Restorer Jill Dunkerton: 'The Death of Actaeon'

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About the video:

Finished or unfinished? National Gallery Restorer Jill Dunkerton studies the X-rays of Titian's 'The Death of Actaeon' to reveal the artist's indecision in painting this masterpiece, while the artist John Lessore explores the theme of his favourite painting in the collection. With actress Lizzy McInnerny performing a dramatic narration of an extract from Ovid's poem 'Metamorphosis'.

John Lessore: In the whole history of art, Titian is my favourite painter and in the National Gallery, this Titian of Diana and Actaeon is my favourite painting. It used to be the Bacchus and Ariadne, but this one has supplanted it. Actaeon quite unwittingly stumbled across Diana bathing in the nude and saw her.

Lizzy McInnerny: Diana dashed some water into the face of the intruder, saying, now go and tell, if you can, that you have seen Diana naked. The hero fled. He could not but admire his own speed, but when he saw his horns in the water, he groaned and tears flowed down the face which had taken the place of his own. When he hesitated, the dogs saw him. He fled and they followed. He longed to cry out, but the words didn’t come. Presently, one fastened on his back. Another seized his shoulder. They were all around him, rending and tearing. It was not until they had torn his life out that the anger of Diana was satisfied.

John Lessore: In this painting, you see he has just started, he’s still a man except for his head, but that’s enough for the dogs. They’re already beginning to tear him to bits. He is no longer their master. He is now their victim.

Jill Dunkerton: The X-ray of 'The Death of Actaeon' shows the most extraordinary number of changes. Sometimes you can make out one of the hounds that we still see in the final painting, for example, that head there, but if you look, there are many more hounds in the X-ray than there are in the painting itself.

There’s a lot of discussion and disagreement about whether a painting like 'The Death of Actaeon' is actually finished. I personally think that at this late stage of his career, Titian himself didn’t necessarily know when pictures were finished. It isn’t lacking any of the final glazes, any of the systematic build-up of colour that you get with earlier pictures and, indeed, with Titian’s earlier pictures, because that was no longer part of his painting process. He is now ranging over the whole surface of the picture. One moment, he is using a glaze; the next moment, he is using an opaque colour. In a sense, it’s unfinished because Titian probably never lived to decide the point at which it was going to be finished, but it’s not unfinished to me in a technical sense. It’s not an incomplete picture and to me it works completely as an image.

John Lessore: Nobody had ever painted in such an abstract, plastic way in which the emotion he is conveying is not conveyed by narrative so much as by shape and movement and colour. What he was doing was incredibly deliberate and refined. It’s just that the handling is so powerful that one gets the impression that the paint is slapped on any old how, which it’s not. It’s certainly not. This is a very late Titian. He must have started it when he was about 70, but gone on with it when he was in his middle 80s. The 10 or 15 years between starting it and finishing it... “finishing” in inverted commas because theoretically it is not finished, but I’m not quite sure that that’s really what Titian felt about it. I think that if he’d wanted to do any more, he would have.

James Heard (in the studio): This is John Julius Angerstein, an important connoisseur of painting. In the 1820s, his collection of 38 pictures became the nucleus of the new National Gallery and included this 'Adoration of the Shepherds', which he believed was painted by the Dutch master Rembrandt. In the harsh light of the gallery’s photographic studio, curator Marjorie Wieseman explains why this is not a signature Rembrandt.

Marjorie Wieseman: This is a painting that has been in the Gallery since the early 19th century. It is a version, or a variant of a painting in Munich that we know was painted by Rembrandt in 1646. And for many years it was thought to be Rembrandt’s, perhaps, preliminary study for that larger painting, or maybe a variance that he made after completing that painting. It’s quite different to the painting in Munich; the composition is reversed. So in the Munich painting, the holy family is on the right and the shepherds enter from the left.

Recently the decision was made to clean the painting to remove layers and layers of discoloured, murky varnish from the painting and some re-paints and see exactly what the painting itself looked like. We gained a lot of definition in the areas of the painting that are painted in this, sort of, shadowy brown. The rafters became much more legible and also the figures over here on the right hand side of the composition. As those details became clearer, it became easier to see that the brushwork and the technique of applying the paint was really quite different from anything Rembrandt ever did.

Our scientific department did some analysis of the materials used in this painting and there’s a very distinctive, sort of canvas preparation, a ground layer, that was only used, so far as we know, by Rembrandt and the artists in his immediate studio, and this painting has that, sort of ground. Rembrandt, throughout much of his career had quite a large studio of artists working with him and working for him. The less experienced young artist would make a very exact copy, as best he could, and the more advanced student would use Rembrandt’s work as the basis for a more creative interpretation. And judging from the extent of the creative departure from the original in this painting, we can probably safely assume that it was done by quite an advanced assistant in Rembrandt’s studio.

James Heard: See this painting and discover many more stories behind National Gallery pictures in Close Examination, Fakes, Mistakes and Discoveries.

04:41

Technical insight

James Heard discusses 'Christ taking leave of his Mother'

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About the video:

See a restoration in action. Wolf Huber's 'Christ taking leave of his Mother', a 16th-century painting, had been badly damaged. Watch the panels get joined carefully back together and the final retouching of losses of paint – with James Heard, National Gallery Education.

James Heard: This fragment of a painting by Wolf Huber, 'Christ taking Leave of his Mother', from around 1520, was acquired by the Gallery in 1995. The Virgin Mary is shown lamenting her son Christ’s departure for Jerusalem, where he will die on the cross. The picture is a fragment of a larger composition. On the far right, Christ’s hand remains, giving the sign of blessing to the Virgin. The panel had evidently been restored within the last 30 years, however, certain details looked odd. After cleaning, the impact of the earlier damage was even clearer. At some time in the past, the joins between the planks had come apart. Before gluing them together again, a carpenter had run a plane along their lengths making a neater join, but losing several millimetres of paint. As a result, the contours were no longer aligned.

Here, a much larger piece of wood is missing. The ends of the fingers are also misaligned. It was decided to take the panel apart so that it could be correctly reassembled. For this operation, the paint is protected with strong tissue paper attached with an acrylic varnish. To replace the wood lost along the joins, new strips were cut from carefully selected and well-seasoned pine.

[Classical music plays]

James Heard: To glue the joins, a special clamping table was used. This enables the conservator to apply gentle, precisely controlled pressure from any direction.

[Classical music plays]

James Heard: Piece by piece, the panel is reassembled. The painting is now varnished and ready for retouching to begin. The retouching is restricted to areas of damage and is carried out using modern pigments in a stable and readily reversible acrylic medium.

[Classical music plays]

James Heard: Finally, the wide insert is restored. At the top and bottom of the wide insert the edges are slightly angled, allowing the new wood and paint to be easily identified.

[Classical music plays]

James Heard: Finally, the painting is put back on display in the National Gallery.

01:44

Close examination

James Heard uncovers 'Woman at a Window'

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About the video:

Discover what was revealed in cleaning this Italian Renaissance painting - with James Heard, National Gallery Education

James Heard: The Gallery owns several paintings which have previously been modified to satisfy changing tastes or interpretations. When 'Woman at a Window' was acquired by the gallery in the mid-19th century it depicted a demure young brunette looking out from behind a curtain. A black and white photograph records the painting in this condition. However, when the heavily discoloured varnish was cleaned off in the conservation studio, it was realised that the picture had been substantially modified. Careful removal in stages of the later surface paint revealed a far more provocative woman.

It became apparent that the original painting by an unknown Italian painter, dated to around 1510 to 1530 had been dramatically altered in the 19th century to satisfy more restrained Victorian tastes. The Renaissance girl’s blonde hair had been switched to brunette, her suggestive sideways glance tamed with wider and more innocent eyes, and her bodice rendered less revealing. The intent of the original Renaissance painting can once again be appreciated after the removal of these falsifying accretions.

Coming soon; Close Examination: Fakes, Mistakes, and Discoveries.

03:41

Technical insight

Watch Conservation's Larry Keith restoring 'The Virgin of the Rocks'

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About the video:

Go behind the scenes at the National Gallery and watch the restoration of 'The Virgin of the Rocks'. Conservation's Larry Keith talks through the restoration of one of Leonardo da Vinci's most elaborate works, which underwent 18 months of specialist treatment to remove a cracked and yellowing varnish.

Larry Keith: The picture was last restored in 1948 and 1949. And unfortunately, the varnish it had had become very foggy; not really so much yellow, but it had lost all its transparency, so it was very hard to see all the dark colours clearly, in particular. And so the decision was taken by the curator and Conservation department and was approved by the Trustees to start the restoration.

What I’m doing now is retouching and we’re just starting this stage. So I’m just filling in the small damages and just starting to block them in a little bit. For a picture of its age, it’s really in remarkably good condition. There are some things that have to do with Leonardo’s technique that have caused some problems with drying and pigment change, but in terms of physical damage, it actually is remarkably well preserved.

All the retouchings that we do in the Gallery are quite reversible and fully documented. You can see them quite clearly in ultraviolet light. And they’re always on top of the varnish so they’re very easily removable and the resins themselves are also quite stable and reversible, although we don’t use exactly the same pigments. Some of the pigments we use are identical – some of the earth colours – because they’re fantastically stable. But other pigments that would have been used by Leonardo and his contemporaries have changed quite a lot and if we used exactly the same material and matched it today, the retouchings would change and so the match wouldn’t hold – it wouldn’t have any longevity.

So what we tend to do is use either the same pigments if they are stable or stable equivalents in terms of transparency and colour. One thing we are pretty careful about trying to do is replicating the layer structures that Old Master painters used because it’s often the optical relationships between underlayers and top coats that give the pictures their distinctive look. It’s not so critical with tiny damages such as the ones I’m doing now, which tend to be one layer on top of a ground and you simply match the colour. But in other areas we really try and replicate the prime and opaque undercolour, and perhaps the transparent glaze on top if that’s what the original picture has because it’s only those relationships between transparent and opaque that have to be reproduced in the retouching – even with modern equivalent materials – that make a retouching successful.

In general, we try and make retouchings quite difficult, if not impossible, to see easily with the naked eye. Although, as I said before, with UV light and with our photographic documentation, they’re very, very easily seen. What we try and do is restore your ability to enjoy the painting, rather than bring attention to the restoration itself.

Panels reunited: Curator Dillian Gordon and Martin Wyld, Head of Conservation, explain how the two pieces of the Umbrian Diptych – The Virgin and Child and The Man of Sorrows – were brought together at the Gallery

View and zoom in on an image of the two panels reunited in Italian, Umbrian, Umbrian Diptych, about 1260

Dillian Gordon: This was a very exciting occasion for the National Gallery. A photograph of ‘The Virgin and Child’ had been sent to Joanna Cannon at the Courtauld Institute and she recognised that it belonged with ‘The Man of Sorrows’, which at some stage of its life has been thought to be Venetian. She’s a friend of mine and when I heard about this I thought it would be an exciting opportunity for the Gallery to acquire these panels because we have very few paintings of the 13th century.

It was always going to be a complicated process because the two panels were obviously in different collections and they hadn’t been together for probably over 100 years. So we were hoping that the owners of each panel would agree to sell to the National Gallery and we could bring the two panels together. And there was a very exciting period over Christmas 1998 to January 1999 when we were negotiating and finally we were successful and the two panels came together.

And of course there’s absolutely no question that they belong together. The backs are painted with imitation porphyry with hooks which definitely fit together and on the front you can see that the punching on both is identical. And the virgin is gesturing towards her child and looking sorrowfully out at the spectator, knowing that the child will be crucified and that he will end up as ‘The Man of Sorrows’ on the Cross.

Miranda Hinkley: So you’ve sort of got life and death on one side and the other.

Dillian Gordon: Yes, very much so. The child, infant Christ as a baby in his mother’s arms, and then the adult Christ with his arms folded in suffering outlined against the Cross, and the angels above are covering their faces in mourning.

Miranda Hinkley: Dillian, you mentioned that originally it had been thought that figure of Christ was thought to be of Venetian origin; has the process of reuniting these panels shed new light on their origin?

Dillian Gordon: Yes, that’s another very exciting aspect. ‘The Virgin and Child’ is unquestionably Umbrian and by putting the two together and realising that in fact ‘The Man of Sorrows’ is Umbrian as well, there are several comparative examples of Umbrian painting, particularly of course with crucifixes, where we can show it’s an Umbrian painter. It’s, of course, an anonymous painter and we don’t know who it was painted for. It’s an object for private devotion. It would have been something that you could perhaps slip into a leather case and travel around with and then open and use for your private prayer. One of the most unusual aspects of this painting is the very elaborate punching that you have all up the borders and around the Virgin’s halo. It’s extremely delicate and, as I say, unusual, for a 13th-century painting at this stage. It becomes much more common in later paintings.

Miranda Hinkley: Very, very delicate isn’t it? You’ve got floral motifs and intertwining plant forms and stems curling round, but each one is very, very delicately done. How would that have been rendered?

Dillian Gordon: The artist would have had an iron tool which he would strike into the gold leaf and depending on the pressure the result would be very slightly different, so sometimes the punches look slightly different but they’ve been made with the same tool.

Miranda Hinkley: Well, when this piece arrived here at the National Gallery, it was in quite a different state to the condition it’s in now. Martin Wyld, you’ve been working on it here in Conservation. Tell us about the condition it was in when it arrived.

Martin Wyld: Well, we could see that it was in very good condition, but it was quite obscured by probably several hundred years worth of varnish and wax polish and dirt settling on it, and at some point when the panels were still together, we think that someone had tried to clean up the figures of Christ and the Virgin and Child and they seem to have pushed all the dirt into the punch marks and incised lines, so instead of having a sort of sparkly punch-marked and incised background, they were like a series of sort of black full stops all over it, and that was the main difference.

Miranda Hinkley: And how have you worked to clean that off?

Martin Wyld: Well, I had to do most of the work under a microscope because as you can see some of the punch marks are about a millimetre across. I’ve been able to use some sort of white spirit and solvent mixed together to soften the black deposits in the punch marks, and then scrape them out with a sharpened stick, working under a microscope at about 15 times magnification. It has taken quite a long time, but I think it’s been well worth it.

Miranda Hinkley: Originally these would have been hinged together so that you could actually close the whole thing up like a book. When you’ve finished the cleaning process how is it going to be presented to people?

Martin Wyld: As they were before, which is they’ll be clamped to a padded backboard right next to each other, which is how they would have originally been seen.

Miranda Hinkley: Well, it’s very exciting to have such exquisite workmanship reunited so visitors can see it as it would have originally been.

Dillian Gordon: You’re quite right. There’s nothing like it in the collection and, indeed, really there’s nothing like it surviving in the world. There are comparatively few 13th-century paintings still surviving in private hands, so we were extremely lucky to be able to buy this. These are objects which in their own right as independent panels are very beautiful and of course reuniting them has made them an object which is absolutely unique.

Miranda Hinkey: When a painting returns to the Gallery after time away in Conservation, its newly cleaned and restored colours are often a revelation. Members of the Conservation team spend a lot of time carefully restoring pictures to their former glory – and it shows. Far less visible, however, is the painstaking effort that goes into repairing what’s underneath the paint surface, which – before canvas became all the rage in the 16th century – was usually a panel made of wood. With this month’s theme in mind, I visited conservator Britta New to find out more, and began by asking her why the team have made caring for panels a speciality.

Britta New: Well, it’s a very important part of our collection. We’ve got about… a third of the works here are actually on panel and the Gallery’s developed a number of different tools and techniques that we can use in their care.

Miranda Hinkley: So why might a panel end up down here for repair then?

Britta New: Well, most of our panels are made from oak or poplar, and each of them have got their own characteristics, but they’ve all got a cellular structure that moves in response to changes in temperature or the moisture content of the air, and we often talk about panels breathing – they contract and expand over periods of time and they can warp in and out as well. At the moment, we’re quite happy with a curved appearance and we tend to allow panels as much freedom of movement as possible.

Miranda Hinkley: So this is where the panel looks as though… I mean, it’s literally curved, it’s slightly sort of buckled, almost…

Britta New: Yes, it tends to bow out in the centre and push out so that it’s got a three-dimensional appearance, rather than a very flat plane like a canvas painting. And as I say, we’re quite happy with that nowadays, but particularly the Victorians didn’t really like that – they wanted to get their paintings to behave themselves and stay flat, and they went to really quite some lengths to get the panels to behave.

They’d often plane down the reverse of a painting, which would make it thinner and more flexible, and then they would stick a wooden lattice structure, what we call a cradle, to the back of the panel and that was designed to keep it flat. The problem was another development in the 19th century was the advent of domestic heating systems and these can make the environmental conditions, like the moisture in the air, fluctuate wildly and this is the sort of thing the panel would be very reactive to. A thinned panel painting would be even more reactive and so the idea of thinning and cradling the painting actually caused an awful lot more problems than having just left the painting by itself.

Miranda Hinkley: And there’s a piece that you’re actually working on at the moment, aren’t you, this 'Virgin and Child in a Mandorla', which is by a follower of Perugino, and that was in a similar condition, wasn’t it? I mean, it almost looks like a kind of corset, strapped to the back of the panel.

Britta New: Yes, it’s as if the panel has been put into a straightjacket. This is exactly what happened to the painting in 1890 when it was last treated and over time the panel had begun to move but it was held firm by the cradle. It began to take on a corrugated appearance relating to the position of where the cradle batons were on the reverse and where the panel had then tried to shrink against the painting, it literally pulled itself to pieces, and it formed these splits that over time became wider and wider. The last photographs we’ve got of this painting were taken in the 1950s and they show some hairline fractures that when I began work had actually developed into open splits.

Miranda Hinkley: So we’ve got these fixed points at the back where the painting is actually attached to the cradle, and those bits are held firm and it’s the bits in between that suffer, and that’s where the splits occur.

Britta New: Yes, precisely.

Miranda Hinkley: So you’re about in the middle of the conservation process now. Can you explain what’s happened so far? It looks like you’ve got a scrapbook here of what’s happened with this panel.

Britta New: Yes, it’s useful to keep documentation of all the work that we carry out. The old varnish was very thick and dark and this was first removed with solvents, and then we glued a tissue paper to the front of the panel, which just protects the paint film while the structural work is being carried out. The cradle was then very gradually pared away from the back using gouges and a metal strap and any remaining glue that was holding the cradle to the panel originally was swollen with a poultice and could then be removed. After we’d removed the cradle, we took off the tissue so that we could see the paint film and then we could make sure that when we did the repair everything would be correctly aligned.

If we don’t do the repairs very well and make sure the surface levels are in alignment and the levels of the painting don’t match up either side of the split, then it’s very hard to disguise that during retouching. Getting the right surface is incredibly important. We had to work on each split, one by one, so we applied the glue and then clamped the splits in position until the adhesive has cured and just worked along the panel until everything was repaired.

Miranda Hinkley: And you’ve actually got a quite hefty piece of machinery to help with this clamping bit of the job.

Britta New: Yeah, we’ve got a special clamping table that was actually designed by my predecessor and it looks a bit like a medieval torture implement, but actually it can do some very delicate work. It can hold the panel in position while we’re working on it and apply varying levels of pressure while we’re working on it at different areas of the panel and just make sure that we can make sure those levels are correct.

Miranda Hinkley: And that’s the stage you’re at now; what happens next, Britta, how do you get this piece back into the collection?

Britta New: Well, we’re in the process of making an auxiliary support for the painting, basically just to support it during framing and handling. It’s basically just a backboard that’s made from the same material as the body of an aircraft because it’s light and it’s inert, and the painting is placed on that with a series of foam blocks behind it. The foam blocks can compress to take up any movement that the painting has and that will provide adequate support for this painting.

Miranda Hinkley: And so presumably that makes it much safer when people come to pick it up and move it around?

Britta New: Yes, absolutely, it’s very important because it’s not just us that will be handling it.

Miranda Hinkley: So once you finish the tray, then presumably the painting goes to restoration and any touching up is done?

Britta New: Yes, I’ll take it back upstairs and then begin the filling and retouching and then it will be able to go back on display, which is quite exciting. Every time you work on something, you spend so long, you actually get to know it really really well, and mentally it becomes your painting, so I suppose when it goes back on display it’s a particular thrill to see something that you’ve worked on up in the Gallery.

Miranda Hinkley: Well, we’ll look forward to seeing it again upstairs. Britta, thank you very much.

Take a trip behind-the-scenes, where conservation's Larry Keith and scientific's Marika Spring explain the cleaning and restoration of Reni's 'Adoration'. How has a set of mysterious marks on the painting's surface presented an additional puzzle?

Miranda Hinkley (in the studio): And now – a trip behind-the-scenes. Upstairs in the Gallery’s attic, away from the noise of Trafalgar Square, the conservation and scientific teams clean and restore paintings. One of the biggest challenges of recent years – in all senses of the word – has been a picture by Guido Reni. Just moving ‘The Adoration of the Shepherds’ around the building requires careful planning – it’s almost 5 metres high and over 3 metres wide. And a set of mysterious marks on its surface have presented an added puzzle. I visited the team to find out more.

Miranda Hinkley (in the Gallery): So I’m here in the Conservation Studio with Larry Keith from Conservation and Marika Spring from Scientific, and we’re looking at ‘The Adoration of the Shepherds’. Tell us a bit about what’s happening in this painting – it’s a nativity scene, isn’t it? And we’ve got Mary and Joseph with the baby Jesus in the centre surrounded by the shepherds.

Larry Keith: Well, as you said, it’s a nativity scene and it’s figures are perhaps slightly bigger than life size. And it’s the holy family surrounded by shepherds and in the middle distance we have another group of shepherds, And in the middle tier there’s a whole assortment of putti hovering above. And it’s quite a big picture – it’s perhaps the largest one we have in the Gallery.

Miranda Hinkley: And what has that meant in terms of moving it around?

Larry Keith: Well, that’s been extremely complicated because it’s actually too big to go through an awful lot of the doors and passageways we need to move the painting into the studio for the restoration work. So we’ve involved a lot of art handling. It’s a rather complicated group effort, because we had to roll this picture, put it into a large roller to actually transport it.

Miranda Hinkley: So when you finally got it up here into the space, what happens next?

Larry Keith: Well the first thing we did was to remove or reduce the old discoloured varnishes and a lot of the old restorations, which again had discoloured and were really getting in the way of viewing the picture. So we would clean it, as we would call that, and after that, we took the picture down to the lower Conservation Studio to do the structural work. After having relined it, we then took it back up to the studio where we are now to varnish the painting. And we’ve started to reintegrate the losses, retouch them, to bring the picture back to the final presentation when it goes down to the galleries again.

Marika Spring: Well, I was involved near the beginning of the conservation treatment, so just after Larry and Paul had removed some of the varnish and when they did this they realised that there were small drips all over the painting - if something corrosive had been splashed across the surface. And they wanted to know what this was, and by knowing what it was, they could then decide how to treat these particular defects. So I took a tiny sample from one of the drips and looked at it under the microscope and then analysed it in a piece of equipment called a scanning electron microscope. And from that we could work out that this wasn’t something that was simply sitting on the surface of the paint; the top part of the paint had actually changed and had been eaten into by this corrosive material. And we could also work out that this corrosive material, from the analysis, we could work out that it contained a lot of phosphorous, and one of the common causes of this type of damage with this particular pattern in drips in churches and historic buildings is from bat urine. As the bats fly past, the urine is deposited on the surface of the painting and bat urine contains a lot of phosphorous, so we think this is probably what happened to the painting, perhaps when it was in its original location.

Miranda Hinkley: And if we look closely at the canvas, particularly in this corner where you’ve got this scene of cherubs or putti, you can actually see little dashes in the paint where that’s happened and it’s like they’ve almost made the pigment darker there.

Marika Spring: Yes, they have. They’ve eaten through the upper layer of paint and we can see the dark ground underneath. But in the sky which is a lighter blue colour it’s had the opposite effect. It’s made little white stripes where it’s damaged and broken up the surface of the paint, so it’s sort of scattering light.

Miranda Hinkley: So Larry, you’ve been touching some of this up – how does that work?

Larry Keith: Well, it’s part of the damage that the paintings had that we try to remove in retouching, which is what we normally do, and Paul Ackroyd and I – who’s working with me on the project – have started the retouching and you can see some areas where we’ve simply just glazed out or toned down the effect of these losses. Each one is very small and not particularly disturbing, but it’s the cumulative effect of literally hundreds of them. It’s a bit like a snowy picture on a TV and if you slowly get rid of them, suddenly you can start to see the painting working properly, and the space moving back and the figures standing properly in front of one another. And it’s very satisfying to see that, at the end of doing quite a bit of it.

Miranda Hinkley: Larry, having the painting here in the conservation studio is also a fantastic opportunity to really have a look at it up close.

Larry Keith: Yeah, it’s one of the great pleasures about working on paintings at The National Gallery as a restorer is that you really get to see them in very good light and in a kind of more intimate way for a brief time while you have them. And then they go and another one comes afterwards. But it’s certainly a wonderful chance to really look closely.

Miranda Hinkley (in studio): Housed beneath a glass ceiling that provides optimal light for their detailed work, the Science and Conservation teams rescue damaged and deteriorating paintings. As part of that role, they study how colours change over time, including a pigment that, as I found out, is notorious for aging badly: yellow lakes.

Miranda Hinkley: I’ve come up to the conservation studios to have a look at a painting that’s being worked on at the moment by Aelbert Cuyp, 'The Large Dort' – a distant view of Dordrecht. It has a view across some fields and in the foreground are some cows and some milkmaids and it’s quite a lovely rural scene. How long has it been with you now?

Larry Keith: I’m not really sure – probably about getting on to a year I think, because we work on a variety of different pictures at once, so it’s not only that picture. But there was quite an extensive amount of work to do, thinking about what was going on and doing a lot of analytical work together with the Scientific department, which helped us proceed; so it was slow progress, I think, for the cleaning.

Miranda Hinkley: And it seems that one of the problems with this painting was in fact his use of yellow?

Marika Spring: That’s correct, yes. All the greens are painted in so-called ‘mixed greens’ which means they’ve used a yellow pigment mixed with a blue pigment to make the green and, particularly in the darker greens, the artist has used a pigment called yellow lake. And yellow lake is made using a plant dye stuff. The most common one in the 17th century was a plant called weld, but the trouble with plant dye stuffs is that they’re very vulnerable to fading and that’s what’s happened in this painting. And when we took a sample from the foreground landscape and looked at it in cross-section, perpendicular to the surface of the paint layers, we could see that the top portion of the paint had faded and turned white and that has the effect of creating a sort of misty veil over the foreground landscape.

Miranda Hinkley: Is this issue with yellow lakes a particular feature of Cuyp’s work?

Marika Spring: It was a very common way of achieving green in the 17th century and he’s not the only artist whose paintings suffer this type of deterioration. But a lot of artists mixed other pigments in as well, which has meant that their paintings haven’t suffered quite so badly. But it is a very characteristic paint defect for paintings by Cuyp, that’s for sure.

Miranda Hinkley: But the overall effect is of this really beautiful mustardy yellow and a very, kind of crackly paint surface. What is this actually an image of?

Marika Spring: This is a very high-magnification detail of the lower right foreground of the painting, and here we can see patches of yellow-brown varnish that are left on the surface of the paint. In fact, the rather nice soft grey colour is actually the result of a pigment change in the paint.

Miranda Hinkley: So that’s yellow lakes at work…

Marika Spring: Yes, that’s yellow lakes again, yes, that are faded.

Miranda Hinkley: So what will be your next step in terms of returning the picture to its former glory?

Larry Keith: Well, after the structural treatment has been done – repairs to the canvas itself – the picture will be revarnished and then we’ll start to fill in any losses with the filler to bring it up to the same surface level. And then we’ll do a retouching using not necessarily identical pigments, but certainly the same kind of layer structures if there’s a grey, and then a brown, and then a translucent yellow in the original, for example, we would repeat the same kind of structure to get the same optical effects, with the intention of making our retouching as difficult to see as possible. That being said, with the understanding that you can always see it very readily with ultraviolet light, and the fact that we also document everything in every stage of the treatment so there’s no intention to deceive in a fundamental way, but simply to make the picture read as harmoniously as possible when it goes back on the wall.